Tylosaurus: From the Shallow Seas of North America

Name: Tylosaurus (Greek for "knob lizard"); pronounced TIE-low-SORE-us

Habitat: Shallow Seas of North Ameria

Historical Period: Late Cretaceous (85-80 million years ago)

Size and Weight: About 35 feet long and seven tons

Diet: Fish, turtles and other reptiles, including dinosaurs

Distinguishing Characteristics: Long, sleek body; narrow, well-muscled jaws

A Large and Vicious Predator

The 35-foot-long, seven-ton Tylosaurus was about as well-adapted to terrorizing sea creatures as any marine reptile could be, considering its narrow, hydrodynamic body, blunt, its powerful head suited to ramming and stunning prey, its agile flippers, and the maneuverable fin on the end of its long tail. This late Cretaceous predator was one of the largest and most vicious of all the mosasaurs—the family of marine reptiles that succeeded the ichthyosaurs, pliosaurs, and plesiosaurs of the earlier Mesozoic Era, and that is distantly related to modern snakes and monitor lizards.

Like one of those extinct plesiosaurs, Elasmosaurus, Tylosaurus figured in the famous 19th-century feud between the American paleontologists Othniel C. Marsh and Edward Drinker Cope (commonly known as the Bone Wars). Squabbling over a set of incomplete Tylosaurus fossils discovered in Kansas, Marsh suggested the name Rhinosaurus ("nose lizard," a great missed opportunity if ever there was one), while Cope touted Rhamposaurus instead. When both Rhinosaurus and Rhamposaurus turned out to be "preoccupied" (that is, already assigned to an animal genus), Marsh finally erected Tylosaurus ("knob lizard") in 1872. (In case you're wondering how Tylosaurus wound up in landlocked Kansas, of all places, that's because much of the western U.S. was submerged beneath the Western Interior Sea during the late Cretaceous period.)

Dazzling Discovery

While Marsh and Cope squabbled endlessly, it was left to a third famous paleontologist, Charles Sternberg, to make the most dazzling Tylosaurus discovery of all. In 1918, Sternberg unearthed a Tylosaurus specimen harboring the fossilized remains of an unidentified plesiosaur, its last meal on earth. But that's not all: an unidentified hadrosaur (duck-billed dinosaur) discovered in Alaska in 1994 was found to harbor Tylosaurus-sized bite marks, though it seems that this dinosaur was scavenged by Tylosaurus after its death rather than plucked, crocodile-style, directly off the shoreline.